Nundasuchus songeaensis
   HOME

TheInfoList



OR:

''Nundasuchus'' is an
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
genus of crurotarsan, possibly a
suchia Suchia is a clade of archosaurs containing the majority of pseudosuchians (crocodilians and their extinct relatives). It was defined as the least inclusive clade containing '' Aetosaurus ferratus'', '' Rauisuchus tiradentes'', '' Prestosuchus ch ...
n
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
related to
Paracrocodylomorpha Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomorpha ...
. Remains of this genus are known from the Middle Triassic Manda beds of southwestern Tanzania. It contains a single species, ''Nundasuchus songeaensis'', known from a single partially complete
skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
, including vertebrae, limb elements, osteoderms, and skull fragments. ''Nundasuchus'' lived in what is now Tanzania, Africa around 240 million years ago. Members of this genus were likely carnivores, around 2.7 to 3 meters (9 feet) long, with ziphodont (
steak knife A steak knife is a sharp table knife designed to efficiently and effectively cut steak. This type of knife comes in a variety of styles and sizes; however, the design often used in a steakhouse typically features a partially serrated blade and w ...
-like) teeth and rows of bony plates ( osteoderms) along their back. Phylogenetic analyses consistently place this genus within the group Crurotarsi based on features of the ankle. Most studies also consider it a pseudosuchian, meaning that it was more closely related to modern crocodilians than it was to dinosaurs. However, ''Nundasuchus'' had an upright stance, with legs situated directly underneath the body, as with various other early pseudosuchians (such as " rauisuchians" and aetosaurs) but unlike modern crocodilians. The classification of ''Nundasuchus'' relative to other pseudosuchians is somewhat controversial. Some phylogenetic analyses place it near or at the base of the group, sometimes along with phytosaurs, based on certain plesiomorphic (primitive) features such as teeth on the palate, a short pubis, and characteristics of the
calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...
(heel bone). Another hypothesis, supported by its original 2014 description, considers it to be somewhat more "advanced" than those groups, instead being closer to ''
Ticinosuchus ''Ticinosuchus'' is an extinct genus of suchian archosaur from the Middle Triassic (Anisian - Ladinian) of Switzerland and Italy. Description One of only a handful of fossil reptiles that have been found in Switzerland, ''Ticinosuchus'' (mea ...
'' and paracrocodylomorphs (the group containing " rauisuchians" and the ancestors of modern crocodilians). This classification scheme is justified by the presence of "staggered" osteoderms, heart-shaped "spine tables", and a groove on the femoral head. Regardless of these hypotheses, it is clear that ''Nundasuchus'' represents a previously unknown group of reptiles with a mixture of features both plesiomorphic and derived with respect to suchian archosaurs.


Discovery

''Nundasuchus'' is known solely from the holotype NMT RB48, a partially complete disassociated and mostly disarticulated individual housed at the
National Museum of Tanzania The National Museum of Tanzania is a consortium of five Tanzanian museums whose purpose is to preserve and show exhibits about the history and natural environment of Tanzania. The consortium developed from the National Museum of Dar es Salaam, es ...
, Dar es Salaam of Tanzania. The holotype consists of a partial right pterygoid, nearly complete right dentary, the right splenial, the right surangular, and isolated teeth, as well as the following
postcrania Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated sk ...
l bones: a partial atlas, two articulated mid- neck vertebrae, two articulated mid- back vertebrae, the last back vertebrae, the
sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...
with sacral
rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...
s, front-most
tail vertebrae The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...
, dorsal ribs, gastralia, articulated and isolated paramedian osteoderms, partial shoulder girdle including interclavicle, parts of both clavicles, complete left and right scapulae, and the right coracoid, the left
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
, both
pubes Pubic hair is terminal body hair that is found in the genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic region around the pubis bon ...
, both femora, the left fibula, inner and outer ends of the left tibia, as well as the left astragalus, left
calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...
, left fourth tarsal and all but fourth metatarsals, and outer ends of right third-to-fifth metatarsals, numerous isolated
phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...
, a partial ungual and many other fragments. NMT RB48 was discovered by Dr. Sterling Nesbitt in 2007 at an isolated outcrop approximately 100 square meters in area known as locality Z41, along with remains of other
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
s and rhynchosaurs. Another locality (Z42) occurs in the immediate vicinity, and yielded four
cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...
s including two unnamed forms, ''
Scalenodon attridgei ''Scalenodon'' is an extinct genus of traversodontid cynodonts from the Middle Triassic of Africa and possibly Russia. The type species ''S. angustifrons'' was named in 1946 and several other species were named in the following years. Most of the ...
'' and ''
Mandagomphodon hirschsoni ''Mandagomphodon'' is an extinct genus of traversodontid cynodonts from the Middle Triassic Lifua Member of the Manda Beds of Ruhuhu Valley, Tanzania. The type species ''Mandagomphodon hirschsoni'' was named by Crompton in 1972 as a species refe ...
'', four dicynodonts including '' Tetragonias njalilus'', ''
Sangusaurus parringtonii ''Sangusaurus'' is an extinct genus of large dicynodont synapsid with two recognized species: ''S. edentatus'' (the type species) and ''S. parringtonii''. ''Sangusaurus'' is named after the Sangu stream in eastern Zambia near to where it was fir ...
'', ''
Angonisaurus cruickshanki ''Angonisaurus'' is an extinct genus of kannemeyeriiform dicynodont from the Middle Triassic of Africa between 247 and 242 million years ago.Hancox, P. John, Kenneth D. Angielczyk, and Bruce S. Rubidge. "Angonisaurus and Shansiodon, Dicynodonts ...
'', and ''
Rechnisaurus cristarhynchus ''Rechnisaurus'' is an extinct genus of dicynodont from the Middle Triassic (Anisian) Yerrapalli Formation of India. It contains a single species, ''Rechnisaurus cristarhynchus''. History ''Rechnisaurus'' has had a long history of confusion w ...
'', and the archosauromorphs '' Stenaulorhynchus stockleyi'' and ''
Asilisaurus kongwe ''Asilisaurus'' ( ); from Swahili, ''asili'' ("ancestor" or "foundation"), and Greek, (, "lizard") is an extinct genus of silesaurid archosaur. The type species is ''Asilisaurus kongwe.'' ''Asilisaurus'' fossils were uncovered in the Manda B ...
''. These localities, located between the Ndatira and Njalila rivers, belong to the fluviolacustrine
mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
- sandstone sequence in the middle of the
Lifua Member The Manda Formation (also known as the Manda Beds) is a Middle Triassic (Anisian?) or possibly Late Triassic ( Carnian?) geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassic, including some of the ...
of the Manda beds of Ruhuhu Basin in Tanzania. Based on comparison with the better studied tetrapod fauna of Subzone C of the ''Cynognathus'' Assemblage Zone of South Africa, this member is considered to date to the Anisian stage of the early Middle Triassic.


Description


Skull

Skull material is very limited for ''Nundasuchus''; only a right lower jaw and a right pterygoid bone (which formed part of the roof of the mouth) were preserved in the holotype. However, even these fragments are informative. The pterygoid is convex when seen from above and concave from below. This ventral (lower) concavity manifests in the form of a deep depression bounded by posterior (rear) and medial (inner) ridges. The portion of the pterygoid which would have been positioned along the midline of the palate is unusual compared to other archosaurs due to possessing teeth. These teeth were small and rounded, placed in three rows parallel to the midline of the mouth. Pterygoid teeth are typically absent in archosaurs, although a few avemetatarsalians ('' Eudimorphodon'', ''
Eoraptor ''Eoraptor'' () is a genus of small, lightly built, basal sauropodomorph. One of the earliest-known dinosaurs, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northwest ...
, Eodromaeus'') and another likely pseudosuchian ('' Turfanosuchus'') are known to have possessed them. The jaw is typical compared to that of most carnivorous archosaurs, being low and long, with serrated, knife-like teeth set in deep sockets. At least 14 teeth were present, with the teeth at the middle of the jaw (around tooth nine) being smaller than those at the front and rear of the jaw. The lower edge of the lateral (outer) side of the jaw was covered in small longitudinal grooves, a feature seemingly unique to ''Nundasuchus'' among early archosaurs. Less unusual is the presence of several rows of pits on the lateral surface and large grooves on the medial surface. The surangular bone at the back of the jaw forms a deeply concave jaw joint preceded by a longitudinal ridge (unique to the genus) and followed by a large, vertically-oriented plate of bone.


Vertebrae and osteoderms

The two incompletely preserved cervical (neck) vertebrae were amphicoelous (concave from both the front and the rear), with a large lateral pit near the base of the neural arch. The concave pleurapophyses (lower rib facets) were near the lower front edge of the vertebrae, while the convex diapophyses (upper rib facets) were positioned higher up. The lower edge of each vertebra possessed a large keel which was deepest towards the rear. Isolated cervical neural spines were similar to those of ''
Batrachotomus ''Batrachotomus'' is a genus of prehistoric archosaur. Fossils of this animal have been found in southern Germany and dated from the Ladinian stage of the Middle Triassic period, around 242 to 237 million years ago. ''Batrachotomus'' was descri ...
,'' being expanded towards their upper front tips into heart-shaped structures when seen from above. Most of the dorsal (back) vertebrae were tall and amphicoelous, and possessed a pair of ventral keels adjacent to the midline, separated by a shallow groove. These ventral keels are similar to those of the unusual aquatic archosauriform ''
Vancleavea ''Vancleavea'' is a genus of extinct, armoured, non- archosaurian archosauriforms from the Late Triassic of western North America. The type and only known species is ''V. campi'', named by Robert Long & Phillip A Murry in 1995. At that time, ...
'', although not as pronounced. Considering that ''Nundasuchus'' is not closely related to ''Vancleavea'', its ventral keels were probably an example of convergent evolution, and they can be considered a unique trait compared to other archosaurs. The rib facets were short, positioned high on the vertebrae at the base of the neural arches. Three ridges radiate outwards from each diapophysis; one connects to the parapophysis, another connects to the main body of the vertebra, and the last one reaches the postzygapophyses (rear vertebral joints). One notable feature of the vertebrae of ''Nundasuchus'' is the possible presence of
hyposphene-hypantrum articulation The hyposphene-hypantrum articulation is an accessory joint found in the vertebrae of several fossil reptiles of the group Archosauromorpha. It consists of a process on the backside of the vertebrae, the hyposphene, that fits in a depression in the ...
s, as reported by the original description. However, a 2018 study doubted this interpretation, arguing that the supposed articulations were actually misidentified components of the zygapophyses. As with the cervicals, the neural spines of the dorsal vertebrae expand outwards into flat structures sometimes called "spine tables". Some dorsals near the hip lose the characteristic ventral keel, instead acquiring additional pits near the rib facets. The
sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...
was probably formed by two unfused vertebrae, connected to massive sacral ribs. The rib facets are huge in conjunction with the sacral ribs, but not large enough to annihilate the pits at the base of the neural arch. Each rib facet of the first sacral vertebra had a distinct upper and lower connection to the trumpet-shaped first sacral rib. The second sacral rib is flatter, and tilts diagonally so that its tapering rear edge is positioned higher than its front edge. A groove is present along the outer edge of this rib, roughly where it would connect to the
ilium Ilium or Ileum may refer to: Places and jurisdictions * Ilion (Asia Minor), former name of Troy * Ilium (Epirus), an ancient city in Epirus, Greece * Ilium, ancient name of Cestria (Epirus), an ancient city in Epirus, Greece * Ilium Building, a ...
. The sacrum in general is similar to that of the
rauisuchid Rauisuchidae is a group of large (up to or more) predatory Triassic archosaurs. There is some disagreement over which genera should be included in Rauisuchidae and which should be in the related Prestosuchidae and Poposauridae, and indeed whethe ...
'' Stagonosuchus,'' except for having thinner neural spines. The caudals (tail vertebrae) near the hip were tall and generally similar to the dorsals, except that their zygapophyses were inclined upwards at a higher angle. Further down the tail, they acquire chevrons and fuse to the caudal ribs, as well as becoming smaller and simpler in general. The dorsal ribs were two-headed, with concave and convex joints corresponding to the convex and concave rib facets of the vertebrae. They were flattened near the vertebrae, and at their tips they had small facets for attachment to the densely packed gastralia (belly ribs). Several groups of osteoderms (plate-like bony scutes) were also preserved in ''Nundasuchus''. Individual osteoderms were lightly ornamented and heart- or leaf-shaped, with rounded edges and tapering front tips. They are similar to those of most other pseudosuchians as well as archosaur relatives such as ''Euparkeria'', but are less elongated than those of some of these taxa, instead being about as wide as they are long. Most of the osteoderms referred to ''Nundasuchus'' are thin bones, with sharply pointed front tips, a thin longitudinal ridge, and a fair amount of overlap. A rare "thick" morphotype is also present, with less overlap, a small and mound-like ridge, and more rounded front tips. At least the "thin"-type osteoderms formed several longitudinal rows stretching along the backbone of the animal. When seen from above, these rows would not have been symmetrical on each side of the animal. Instead, they were "staggered", with the left and right rows slightly offset from each other. An estimated five osteoderms were present per every two vertebrae.


Pectoral girdle and forelimbs

The scapula (shoulder blade) was paddle-like and somewhat small. The lower portion of the scapula is where the glenoid (shoulder socket) is located, pointing backwards from the rear edge of the bone. This general area is the widest part of the bone when seen head-on, and underlies the thinnest part when seen from the side. Directly above the glenoid lies a small pit, likely the origin point of the triceps muscle. Meanwhile, the front edge of the scapula has a distinct ridge, probably the acromion process. The scapula of ''Nundasuchus'' differs from advanced pseudosuchians due to its small triceps pit, but also from phytosaurs due to its distinct acromion. The lower edge of the scapula connects to the semicircular coracoid bone. The rear portion of the coracoid extends back and curves upwards to form the lower half of the glenoid, but is not offset from the socket by a distinct notch. However, a wide groove is present below the glenoid when seen from the side, similar to the case in aetosaurs and ''Postosuchus''. In front of the glenoid, a hole known as the coracoid foramen pierces the coracoid, and, in a feature unique to ''Nundasuchus'', this hole is surrounded by several knob-like structures. Other fragments of the pectoral girdle, such as an interclavicle and clavicles, are also preserved. They are covered in grooves, with thin, blade-like edges. The interclavicle is spoon-shaped, concave from above and convex from below, although its true shape is unknown due to the rear portion being broken off. Overall it is more similar to those of paracrocodylomorphs rather than phytosaurs. The only portion of the forelimb known for this genus was the
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
(upper arm bone). Its medial edge was concave while the lateral edge was almost straight as in phytosaurs. In conjunction with this, the deltopectoral crest (a large flattened structure near the
humeral head The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a round ...
) is oriented more anteriorly than laterally. Both the humeral head and the tip of the
lower extremity The human leg, in the general word sense, is the entire lower limb of the human body, including the foot, thigh or sometimes even the hip or gluteal region. However, the definition in human anatomy refers only to the section of the lower lim ...
of the bone were covered with deep grooves. Just above the lower extremity was a depression, and just lateral to this depression was a distinct ectepicondylar groove.


Pelvic girdle and hindlimbs

The only preserved part of the pelvic girdle (hip), not counting the sacrum, was the left pubis bone. This bone was characteristically small in ''Nundasuchus'', only about 30% the length of the femur. This is comparable to phytosaurs, aetosaurs, and early avemetatarsalians, but in contrast to the condition in other archosaurs. The areas where the pubis would have contacted other bones of the hip are broken, but evidently the pubis did possess features such as an inset obturator foramen and an insertion for the ambiens muscle under the
acetabulum The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Structure There are three bones of the ''os coxae'' (hip bone) that c ...
(hip socket). The main shaft of the pubis is not strongly expanded in most directions, but the medial edge has a plate-like inner extension known as a pubic apron, which would have contacted the corresponding extension on the right pubis. This pubic apron is convex when seen from the front. The femur (thigh bone) is sigmoidal (S-shaped), with the femoral head being twisted slightly inwards and the distal condyles being twisted slightly outwards. This creates an angle of 45 degrees between these two extremities of the bone, as with most eucrocopodans apart from dinosaurs. As with other eucrocopodans, the femoral head has several distinct tubera (bumps), one on the anterolateral surface of the bone and another on the posteromedial surface. ''Nundasuchus'' also may have had a third tuber on the medial surface of the head as in
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
s, but this portion of the bone is damaged so it cannot be assessed with certainty. The femoral head also has a groove on its upper surface, similar to paracrocodylomorphs. Further down the posteromedial face of the shaft is a long, sharp ridge known as the fourth trochanter. About 40% down the front part of the shaft is a tuber covered with grooves. This bump was likely an attachment point for the ''iliofemoralis'' muscle which helped to stabilize the hip. The distal part of the femur has a large crista tibiofibularis, an upper extension of the lateral condyle. Both the crista and the medial condyle are large, and taper into rounded apices. In addition, the lateral and medial condyles each have a small depression at their extemities, with that of the medial condyle likely corresponding to the ''femorotibialis'' muscle. The proximal part of the tibia (inner shin bone) is roughly diamond-shaped in cross section, with rounded lateral and medial tubera as well as a low and indistinct forward-pointing ridge known as a cnemial crest. The lateral tuber is larger and more concave, like that of ornithosuchids. Apart from these tubera, the proximal part of the tibia is mostly convex. However, a distinct notch is present behind the lateral tuber. This is probably an attachment point for ''flexor tibialis internus'' muscle. The distal part is smooth and oval-shaped in cross section and 'flexed' when seen from behind. The fibula (outer shin bone) is sigmoidal, with a flattened medial surface, a large crest for the ''iliofibularis'' muscle on the lateral surface, and a distal face which tilts forwards. The foot consisted of five metatarsals attached to
phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...
(toe bones). The smallest metatarsal was the innermost one (I), with metatarsal II being longer and III being longer than either. Although metatarsal IV is incomplete, it has been estimated to be longer than III. This would be highly unusual among Triassic reptiles, of which only ''Proterosuchus'' shares this characteristic. Metatarsal I is somewhat squashed diagonally, with the edge facing the rest of the foot being positioned higher than the inner edge. A crest is also present on the inner edge. The articulation with the ankle is convex and expanded towards the rest of the foot. Metatarsal II is parallelogram-shaped in cross section, with a 'lip' on its upper edge that accepts the first metatarsal. Metatarsal III has the largest distal joint while IV has the smallest, indicating that the third toe was more massive than the fourth. Metatarsal V is hook-shaped, with two distinct proximal articulations for the fibula and the fourth distal tarsal of the ankle. The phalanges are generally robust, but those of the fifth toe were longer and hourglass-shaped, attached to a rough-textured ungual (claw). In general, the foot bones resemble those of ''Prestosuchus'' and phytosaurs.


Ankle

The ankle was primarily formed by two bones, the
calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...
on the outer side and the astragalus on the inner side. These bones and their joints clearly show distinguishing features of the group Crurotarsi, which includes suchians, phytosaurs, and probably avemetatarsalians. For example, the calcaneum's attachment with the astragalus is concave, and the calcaneum also has a cylindrical extension with flared edges, known as a calcaneal tuber. The calcaneal tuber is directed about 45 degrees between sideways and backwards, similar to phytosaurs and non-archosaurian eucrocopodans, but in contrast to most other suchians, which have calcaneal tubera oriented more backwards. On the other hand, the length of the calcaneal tuber is moderate, similar to that of typical pseudosuchians rather than the much more elongated structure of phytosaurs. The lateral side of the tuber has a noticeable 'pad', which is seemingly unique to ''Nundasuchus''. The upper surface for the calcaneum connects to the fibula with a convex, barrel-shaped joint. This is also similar to phytosaurs and suchians but in contrast to ornithosuchids, where this joint is more dome-like. Both the fibular and astragalar facets of the calcaneum are a continuous surface, a condition unlike suchians. The upper surface of the astragalus has a triangular facet for the fibula as well as a larger, oval-shaped facet for the tibia. The tibial facet is divided into two basins by a low convexity, although this flexion is somewhat indistinct compared to that of suchians and avemetatarsalians. The calcaneal facet comes in the form of a flat surface overlying a convex 'peg', a feature characteristic of crurotarsal joints. The peg is poorly developed, more similar to that of phytosaurs rather than other suchians. The front edge of the astragalus has a large concave surface (astragalar hollow) overlying a small convexity (astragalar ball). The astragalar ball is approximately as well developed as that of the aetosaur '' Longosuchus''.


Etymology

''Nundasuchus'' was first described and named by Sterling J. Nesbitt, Christian A. Sidor, Kenneth D. Angielczyk, Roger M. H. Smith and Linda A. Tsuji in
2014 File:2014 Events Collage.png, From top left, clockwise: Stocking up supplies and personal protective equipment (PPE) for the Western African Ebola virus epidemic; Citizens examining the ruins after the Chibok schoolgirls kidnapping; Bundles of wat ...
and the type species is ''Nundasuchus songeaensis''. The generic name is derived from
Swahili Language Swahili, also known by its local name , is the native language of the Swahili people, who are found primarily in Tanzania, Kenya and Mozambique (along the East African coast and adjacent litoral islands). It is a Bantu language, though Swahili ...
''nunda'' meaning " predator", plus ''suchus'' from Greek ''soukhos'', an Egyptian crocodile god. The new
specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...
refers to the provincial capital of Songea, located near to the collection locality of the remains, as indicated by the Latin suffix ''-ensis'', meaning "from".


Classification

The original description of ''Nundasuchus,'' Nesbitt ''et al.'' (2014), tested its phylogenetic position using the two most comprehensive early
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
phylogenetic datasets available. The first dataset used was a version of Brusatte ''et al.'s'' 2010 archosaur phylogeny which had been updated by Butler ''et al.'' (2011) during a study on the anatomy of ''
Ctenosauriscus ''Ctenosauriscus'' is an extinct genus of sail-backed poposauroid archosaur from Early Triassic deposits of Lower Saxony in northern Germany. It gives its name to the family Ctenosauriscidae, which includes other sail-backed poposauroids such as ...
''. The second dataset was a more comprehensive and widely accepted study on archosaur relationships created by Nesbitt in 2011. Both analyses found that ''Nundasuchus'' was a pseudosuchian, meaning that it was an archosaur more closely related to crocodilians than it was to dinosaurs. This identification was primarily based on traits of the ankle which were shared between ''Nundasuchus'' and pseudosuchians. The Brusatte ''et al.''(2010) dataset placed it as the most
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...
pseudosuchian (although the name "Crurotarsi" was used for the group), less crownward (further from crocodilians) than even the phytosaurs. Nesbitt ''et al.'' (2014)'s application of the Nesbitt (2011) dataset placed ''Nundasuchus'' more crownward, compared to its position in Brusatte ''et al.'''s results. Nesbitt (2011) considered
crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cr ...
(crocodilian ancestors) to have been descended from taxa traditionally identified as " rauisuchians". Since Rauisuchia typically omits crocodylomorphs and would therefore be
paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
with his results, Nesbitt decided to scrap the name, replacing it with the
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
clade
Paracrocodylomorph Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomorp ...
a. This clade itself is allied with the
Swiss Swiss may refer to: * the adjectival form of Switzerland * Swiss people Places * Swiss, Missouri * Swiss, North Carolina *Swiss, West Virginia * Swiss, Wisconsin Other uses *Swiss-system tournament, in various games and sports *Swiss Internation ...
suchian ''
Ticinosuchus ''Ticinosuchus'' is an extinct genus of suchian archosaur from the Middle Triassic (Anisian - Ladinian) of Switzerland and Italy. Description One of only a handful of fossil reptiles that have been found in Switzerland, ''Ticinosuchus'' (mea ...
'' based primarily on similarities of the ischium. When ''Nundasuchus'' was added into the dataset, it was placed as the sister taxon to the ''Ticinosuchus'' + Paracrocodylomorpha clade. This was justified by three traits: heart-shaped "spine tables", a groove on the proximal side of the femoral head, and "staggered" osteoderms. Nesbitt ''et al.'' (2014) questioned these results due to the fact that ''Nundasuchus'' possesses many
plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and ...
archosaurian traits (i.e. typical for very basal archosaurs) that appear to be autapomorphies (unique features), if it is truly a member of Pseudosuchia. These include palatal teeth, a short pubis, and a calcaneal tuber which is not as strongly deflected backwards. Thus, they performed further analyses under certain relationship constraints, such as forcing ''Nundasuchus'' to be outside Archosauria or closer to Phytosauria. These analyses revealed little change in the relationships (apart from the constraints themselves), but major changes to the traits associated with these relationships, changing the traits that were considered to diagnose Pseudosuchia, Archosauria, and other
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
s. Therefore, it is not clear whether ''Nundasuchus'' is a suchian that has convergences with far more basal archosaurs as the two phylogenetic analyses suggest, or an
archosauriform Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthier ...
closely related to Archosauria, with features convergent to the morphology of the more advanced paracrocodylomorphs. However, support for the placement of ''Nundasuchus'' does weaken the further away it is placed from Paracrocodylomorpha. The results of the unconstrained analysis of Nesbitt ''et al.'' (2014) using the Nesbitt (2011) dataset are simplified below (the relations within bolded
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
s are not shown). In 2016, ''Nundasuchus'' was featured in Martin Ezcurra's study of archosauromorphs, and was placed into a phylogenetic analysis similar is size and scope to Nesbitt (2011). Contrary to the results of Nesbitt ''et al.'' (2014), Ezcurra (2016) placed ''Nundasuchus'' as a basal pseudosuchian, although not quite as basal as Phytosauria. He also discussed the three features which those authors used to justify placement of ''Nundasuchus'' near Paracrocodylomorpha. Heart-shaped spine tables, for example, were considered to have had an erratic distribution within Pseudosuchia, with some taxa (such as
gracilisuchids Gracilisuchidae is an extinct family of suchian archosaurs known from the early Middle Triassic to the early Late Triassic (Anisian – early Carnian) of China and Argentina. Distribution Currently, the oldest known gracilisuchid is ''Turfanosuc ...
) lacking them and others (i.e. phytosaurs and ''Batrachotomus'') having them in only certain vertebrae. Likewise, staggered dorsal osteoderms were only found to be present in ''Nundasuchus'' and ''Gracilisuchus'', with none of the sampled paracrocodylomorphs sharing the trait. He did concede that a groove on the femoral head is consistent with the hypothesis of ''Nundasuchus'' being close to paracrocoylomorphs, as the trait is also found in '' Prestosuchus'' and ''Batrachotomus''. However, Ezcurra also admitted that his analysis was more focused on basal
archosauromorphs Archosauromorpha ( Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, lizard ...
and archosauriforms rather than true archosaurs, and therefore it may not be completely accurate for crownward groups such as pseudosuchians. He noted that certain taxa crucial to Nesbitt (2011)'s results, such as ''Ticinosuchus'' and ''Saurosuchus'', were omitted from his study. These genera were paracrocodyomorphs which possessed staggered osteoderms, heart-shaped spine tables, and a groove on the femoral head, therefore justifying a close relationship to ''Nundasuchus''. In 2018, another early paracrocodylomorph, '' Mandasuchus'', received a long-awaited formal description. This genus also had these three features identified by Nesbitt ''et al.'' (2014). A phylogenetic analysis was included in the description, based primarily on Nesbitt (2011) but also including new data from the ''Nundasuchus'' description as well as a recent study on gracilisuchids. The results found that either ''Nundasuchus'' or gracilisuchids were the sister taxa to Paracrocodylomorpha+''Ticinosuchus'', although it could not precisely determine which one was closer. An updated version of the Nesbitt (2011) dataset published by Da-Silva ''et al''. (2018) placed ''Nundasuchus'' at the base of Pseudosuchia. This study incorporated many recent revisions and additions to Nesbitt's methodology, though its results more closely resembled those of Ezcurra (2016) rather than Nesbitt (2014).


References

{{Taxonbar, from=Q18908063 Triassic archosaurs Middle Triassic reptiles of Africa Anisian life Triassic Tanzania Fossils of Tanzania Fossil taxa described in 2014 Prehistoric pseudosuchian genera